Twice in the past week, Miami residents have been treated to the nighttime sound of Blackhawk helicopters thundering between downtown Miami skyscrapers.

Federal authorities say that Special Operations military units in cooperation with the Department of Homeland Security and Miami-Dade County law enforcement officers conducted two 'military' drills special operations drills this week. The statement said that, 'the drills were a part of a joint emergency preparedness exercise.'

The statement added that the remaining purposes of the drills are 'classified'.